Magnetic recording medium, method of fabricating magnetic recording medium, and magnetic storage.
The present invention relates to magnetic storage used as auxiliary storage for a computer, or the like, a magnetic recording medium used for the magnetic storage, and a method of fabricating the magnetic recording medium.
With progress of information-oriented society, the amount of information daily used is steadily increasing. Demand for high density recording and large memory capacity for magnetic storage is accordingly growing. An inductive head using voltage change in association with magnetic flux change with time is used as a conventional magnetic head. Both recording and reproduction are performed by one head. In recent years, a composite head having a head for recording and a head for reproduction, in which an MR (magnetic resistive) head with higher sensitivity is used as the reproduction head, has rapidly increased in use. In the MR head, change in electric resistance of a head device in association with change in magnetic flux leaked from a magnetic recording medium is used. A head with higher sensitivity using a very large magnetic resistive change (giant magnetic resistive effect or spin valve effect) which occurs in a plurality of magnetic layers laminated via non-magnetic layers is being developed. According to the head, change in electric resistance which is caused by change in relative directions of magnetization of the plurality of magnetic layers via the non-magnetic layers by the magnetic field leaked from a medium is used.
In magnetic recording media which are practically used at present, alloys containing Co as a main component, such as Coxe2x80x94Crxe2x80x94Pt, Coxe2x80x94Crxe2x80x94Ta, Coxe2x80x94Nixe2x80x94Cr, and the like are used for a magnetic layer. Each of the Co alloys has a hexagonal close-packed (hcp) structure in which a c-axis direction is an easy axis of magnetization, therefore a crystal orientation such that the c-axis of the Co alloy is the longitudinal direction, that is, (110) orientation is desirable as a longitudinal magnetic recording medium for reversing the magnetization in the magnetic layer and recording. The (110) orientation is, however, unstable, so that when the Co alloy is formed directly on a substrate, such an orientation is not generally obtained.
A method in which the fact that a Cr (100) plane having a body-centered cubic (bcc) structure has good lattice matching with a Co (110) plane is used, a (100) orientated Cr undercoating layer is first formed on a substrate, and a Co alloy magnetic film is epitaxially grown, thereby obtaining the (110) orientation such that the c-axis of the Co alloy magnetic film is orientated to the in-plane direction. Also, a method in which a second element is added to Cr to improve the crystal lattice matching performance in the boundary face between the Co alloy magnetic film and the Cr undercoating layer and intervals of lattices in the Cr undercoating layer is widely used. The Co (110) orientation is further improved and coercive force can be increased. There are examples of adding V, Ti, and the like.
Another factor necessary to realize high recording density is reduction in noises as well as increase in coercive force of the magnetic recording medium. Since the MR head has extremely high reproduction sensitivity, it is suitable for high density recording. However, the MR head is sensitive not only to reproduction signals from the magnetic recording medium but also to noise. Consequently, in the magnetic recording medium, it is required to reduce noise more than in a conventional technique. It is known that in order to reduce the medium noise, it is effective to have fine and uniform grain size of the magnetic film or the like.
Another important factor is improvement in shock resistance, especially when magnetic disk apparatuses are being mounted on portable information devices such as notebook-sized personal computers or the like in recent years. Therefore, improvement in the shock resistance is a very important subject from the viewpoint of improving reliability. A glass substrate whose surface is strengthened or a crystallized glass substrate is used in place of a conventional Al alloy substrate to which Nixe2x80x94P is plated on the surface, thereby enabling the shock resistance of the magnetic disk medium to be improved. Since the surface of the glass substrate is smoother than that of the conventional Nixe2x80x94P plated Al alloy substrate, it is advantageous to reduce floating spacing between a magnetic head and the magnetic recording medium and is suitable to obtain high recording density. In case of using the glass substrate, however, problems of poor adhesion with the substrate, invasion of impurity ions from the substrate or absorption of gas on the surface of the substrate into the Cr alloy undercoating layer, and the like occur. As a countermeasure, any of the various metal films, alloy films, and oxide films can be formed between the glass substrate and the Cr alloy undercoating layer.
Japanese Patent Application Laid-Open Nos. 62-293511, 2-29923, 5-135343, and the like are techniques related to the above.
It is known that, as mentioned above, reducing and having uniform grain size of the magnetic film is effective in reducing the medium noise. However, when a magnetic disk apparatus was produced experimentally by combining a magnetic recording medium with a recording density of about 900 megabits per square inch and a high-sensitive MR head according to the conventional technique, sufficient electromagnetic conversion characteristic by which 1 gigabit or higher recording density per square inch can be obtained could not be obtained. Especially, when the glass substrate was used as a substrate of the magnetic recording medium, poor electromagnetic conversion characteristic in a high recording density area resulted. The cause was examined and it was found that the Cr alloy undercoating layer formed directly or via various metal or alloys as used in the conventional techniques on the glass substrate was not orientated as strong (100) as that in the case where it was formed on the Nixe2x80x94P plated Al alloy substrate. A crystal plane except for (110) of the Co alloy magnetic film is grown in parallel to the substrate and the in-plane orientation of the c-axis as an easy axis of magnetization was small. Thus, the coercive force was reduced and a reproduction output with the high density recording deteriorated. In the case of using the glass substrate, the grain in the magnetic film was larger than that of the Al alloy substrate and the distribution of grains was larger by 20 to 30%. The medium noise was therefore increased and the electromagnetic conversion characteristic deteriorated. Even if an amorphous film or a fine crystal film disclosed in Japanese Patent Application Laid-Open No. 4-153910 was formed between the glass substrate and the undercoating layer, the size of the grain in the magnetic film was sometimes reduced to a certain degree but was not sufficiently reduced. It was not effective with respect to the reduction in the grain distribution, and preferable electromagnetic conversion characteristic could not be obtained.
It is a first object of the invention to provide a magnetic recording medium having low noise level in which orientation of a magnetic film is improved and the grains in the magnetic film are fined and uniformed.
It is a second object of the invention to provide a method of fabricating the magnetic recording medium.
It is a third object of the invention to provide a magnetic storage with high recording density.
In order to achieve the first object, according to a magnetic recording medium of the invention, a first undercoating layer is deposited directly or via a third undercoating layer on a substrate, a second undercoating layer is directly deposited on the first undercoating layer, and a magnetic film is deposited on the second undercoating layer. Clusters having a large amount of oxygen are spread on the boundary face of the first and second undercoating layers.
In order to achieve the second object, according to a method of fabricating a magnetic recording medium of the invention, a first undercoating layer is formed on a substrate directly or via a third undercoating layer and is exposed to an atmosphere including oxygen for a time period that PO2.t (where, PO2.t is oxygen partial pressure of the atmosphere and t is time of exposure of the substrate to the atmosphere) is in a range from 1xc3x9710xe2x88x926 (Torrxc2x7sec) to 1xc3x9710xe2x88x921 (Torrxc2x7sec), a second undercoating layer is directly formed on the first undercoating layer exposed to the atmosphere, and a magnetic film is formed on the second undercoating layer.
In order to achieve the third object, a magnetic storage of the invention comprises: the above-mentioned magnetic recording medium; a magnetic head constructed by a recording part and a reproducing part provided in correspondence to the faces of the magnetic recording medium; a drive unit for changing relative positions of the magnetic recording medium and the magnetic head; a magnetic head driving unit for positioning the magnetic head to a desired position; and a recording and reproduction signal processing system for inputting signals to the magnetic head and reproducing output signals form the magnetic head.
It is preferable that the first undercoating layer is made of an alloy consisting of two or more kinds of elements. In the case where elements which oxidize differently are included in the alloy and the first undercoating layer is exposed to an atmosphere at a certain oxygen partial pressure for a certain time, it is estimated as follows. A uniform oxide film whose surface is continuous in the plane is not formed but clusters having a large amount of oxygen are locally formed in an area rich in the element which is easily oxidized and become the nucleation of the second undercoating layer. The grains of the second undercoating layer grown on the clusters are fined and uniformed and further, the average grain size of the magnetic film is reduced and the grain diameter is uniformed.
The magnetic recording medium of the invention has effects on reduction in medium noise, increase in coercive force, and the like. According to the method of fabricating the magnetic recording medium of the invention, the above magnetic recording medium can be easily fabricated. The magnetic storage of the invention using the magnetic recording medium has high recording density.
Providing of oxidizing step in a process sequence of fabricating a magnetic disc is known by U.S. Pat. No. 4,552,820.
The purpose of oxidation in the invention is to reduce a modulation of reproduction output. The modulation is a kind of fluctuation in reproduction output due to anisotropy of crystal structure occurring in a sputtering apparatus of an in-line type (method of depositing films while conveying, that is, moving a substrate in one direction). Since a sputtering apparatus of a stationary facing type (method of depositing films while a substrate and a target stationarily face each other) is mainly used at present, the problem is ignored. Even in the sputtering apparatus of the in-line type, since a film thickness of an undercoating layer and that of a magnetic layer are reduced as the recording density becomes higher, the problem of the modulation is small. The present invention intends to reduce noise by uniforming the orientation of the crystal and is different from the above U.S. patent. According to the above U.S. patent, by oxidizing an Nixe2x80x94V layer before depositing a Cr layer as an undercoating layer, the grain size of the Cr film is increased, thereby reducing the modulation. On the contrary, according to the present invention, clusters are generated by oxidization in a step prior to formation of the Cr alloy undercoating layer, and the grain size of the Cr alloy undercoating layer is reduced, thereby realizing reduction in noise.